undefined = '123'
console.log(undefined === void(0),'undefined')
console.log(void console.log('abc'))  //会打印出abc
console.log(void 66+99) //先执行void66,结果为undefined，在执行undefined+99，结果为NaN
console.log(void (66+99))
function test(){
    let undefined = '123'
    console.log(undefined)  //123
}
test()

console.log(void(66+99))
console.log(void(0))
